1. Field of the Invention
The present invention relates generally to a restrained joint for coupling plastic pipe and, more specifically, to an improved belling process for the integral manufacture of such a restrained joint in the socket end of a thermoplastic pipe, fitting or coupling.
2. Description of the Prior Art
A variety of piping systems are known for the conveyance of fluids which employ elastomeric type sealing rings or gaskets. The pipes used in such systems may be formed of PVC, polyolefins such as PE and PP, ductile iron, concrete, clay, fiberglass, steel, cast iron, fiberglass/cement reinforced pipes and such metals as aluminum and copper. At the present time, pipes formed of thermoplastic materials, including PVC and polyethylene, are increasingly preferred for use in new pipeline installations for below ground pressure piping such as might be encountered in municipal water systems.
In forming a joint between thermoplastic sections of pipe of this general type, the spigot or male pipe end is inserted within the female or socket pipe end. An annular, elastomeric ring or gasket is typically seated within a groove formed in the socket end of the thermoplastic pipe. As the spigot is inserted within the socket, the gasket provides the seal capacity for the joint. In some instances, it is necessary to provide a “restrained joint” to insure the spigot or male pipe end and the female or socket end do not separate due to hydraulic forces that exist inside the pipeline.
The need to restrain lengths of pipe coupled together in this general fashion exists not only with respect to municipal water lines, but in other diverse applications including well casings, directional drilling applications, laying of fiber optic cable, and above ground pressure piping applications. Over time, various solutions have been proposed for providing the needed restraining function for such applications.
In the area of well casings and directional drilling applications using PVC pipe, one approach has been to use axially aligned circumferential grooves machined into the mouth region of the belled pipe end and into the exterior surface of the mating male, spigot pipe end. A port is drilled through the female bell to complete a circumferentially shaped, canal type passageway for receiving a locking key strap which is subsequently passed through the bell wall, into the canal of the aligned grooves, and around the circumferential passageway.
A number of different variations of this general concept are known in the marketplace at the present time. For example, U.S. Pat. No. 5,662,360 discloses an interlocking restraint plastic pipe joining system which includes pairs of female and male integral end connections. The female end connection has at least one depression within a mouth opening thereof. The male end connection has at least one protrusion formed on an exterior surface thereof which is adapted to matingly engage, in a snap fit fashion, the depression in the mouth opening of the female member.
U.S. Pat. No. 6,086,279 describes the equipment used in a manufacturing process for machining grooves into the inside surface of the female bell member of a plastic pipe coupling. Other patents representative of the general state of the prior art describe various purported improvements to this basic concept, while sharing the common element of machining one or more grooves into the inner mouth region of the belled pipe end.
U.S. Pat. No. 6,352,288 shows a mechanical pipe connection that includes the feature of coupler recesses with discontinuous locking grooves on the pipes. The interlocking system may also include male and female portions which mechanically mesh together to form binding contact between the pipes to reduce the individual rotation of the pipes relative to one another. Similarly, U.S. Pat. No. 5,255,945 discloses a system for connecting sections of plastic tubing which form a sampling pipe for a well, in which a nose of one tube engages a sleeve on the neighboring tube. The system is represented as being an improvement to the tangential-key type of tube jointing system, where a flexible key passes through a key-hole in the sleeve, and around the circumference of the key-groove. This design includes a rectangular key in place of the usual round key. Also shown is an O-ring seal, which resides in a seal-groove cut in the nose, outboard of the key-groove.
U.S. Pat. No. 6,325,424 teaches a coupling assembly for conduit or pipe comprising a first coupling member, a second coupling member and a locking member. The first coupling member is optionally a tubular component and the second coupling member or coupler is optionally a belled component. The invention is also provided with an annular sealing member.
In each of the above described example conduit and pipeline applications, it is desirable that the joint be air and water tight. For example, when pulling fiber optic cable through a conduit, it is a common practice to use air pressure to first blow a fine fish-string through the pipeline. Also, where electrical wire or fiber optic cable is located inside the pipeline, the pipeline joints need to prevent infiltration of ground water. In similar fashion, well casing applications need to prevent infiltration of percolated surface water that potentially contains contaminants. Temporary pressurized and gravity waterlines must also remain water tight for most usable applications.
Due to certain inherent design limitations, most of the currently employed manufacturing techniques for machining grooves into the interior mouth region of the female, belled pipe end or section use a square shaped groove to house an O-ring shaped sealing gasket. It is well understood that, by definition, machining a groove into interior surface of the belled pipe end reduces wall thickness, thereby reducing pipe wall strength. To minimize the depth of the groove, O-rings are most commonly used as the sealing member. U.S. Pat. No. 5,255,945 provides a detailed explanation of these design constraints. U.S. Pat. No. 6,325,424 describes a sealing gasket or element that is generally rectangular in cross-section, residing in a machined groove having a lesser relative depth, which addresses the pipe wall thickness limitation, but with only limited success.
In those joints having circumferential grooves machined into the inside inwardly facing surface of the female bell end and machined into the outside outwardly facing surface of the male spigot end and a port drilled through the female bell, it is necessary to align the port with the groove of the outwardly facing surface of the male spigot during installation by the contractor. Without a positive stop of some type provided by the male and female mating pipe ends, available art often relies on the contractor in the field using visual estimates to make this alignment.
Thus, despite the various advances which have been made in the above described technologies, a need continues to exist for an improved joining system for use in assembling a restrained joint formed between two sections of plastic pipe that can withstand anticipated axial, and/or radial forces, as well as transitory shocks which may be encountered in the environment of use.
A need also exists for such a pipe joining system which is economical to implement so that it does not greatly increase the cost of manufacture of the piping system.
A need exists for such a joining system which the restraint portion of the system works independently of the seal and can thus accept differing seal profiles.
A need exists for such a joining system which is comprised of components which can be mounted on a forming mandrel and which can be belled over in a Reiber style manufacturing operation.
A need exists for a joining system for restrained joint which can meet the needs of such diverse plastic pipe conduit or pipeline applications as above ground temporary water lines, municipal water lines, well casing applications and horizontal drilling applications.